Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.
You must implement a solution with linear runtime complexity and use only constant extra space.
Example 1:
Input: 2 2 1 Output: 1
Example 2:
Input: 4 1 2 1 2 Output: 4
Example 3:
Input: 1 Output: 1
Constraints:
- 1 ≤ nums.length ≤ 3 × 10⁴
- -3 × 10⁴ ≤ nums[i] ≤ 3 × 10⁴
- Each element appears exactly twice except for one element.
Input format: A single line of space-separated integers.
Output format: A single integer.